Flexor Pollicis Brevis

Origin

The flexor pollicis brevis muscle consists of two heads:

- a large superficial head, which originates from the tubercle of trapezium bone and the flexor retinaculum of hand;

- a small deep head, which originates from the palmar aspects of the capitate and trapezoid bones.

Insertion

The muscle bellies of the superficial and deep heads of flexor pollicis brevis travel inferiorly and converge to a single tendon. This tendon contains a sesamoid bone and inserts onto the lateral aspect of the base of the proximal phalanx of thumb.

Key Features & Anatomical Relations

The flexor pollicis brevis muscle is found in the thenar compartment of the hand. It is a short skeletal muscle. It is located:

- anterior (superficial) to the opponens pollicis muscle;

- posterior (deep) to the recurrent branch of median nerve;

- medial to the abductor pollicis brevis muscle;

- lateral to the palmar aponeurosis.

The superficial head lies anterior to the tendon of the flexor pollicis longus, while its deep head lies posterior to the tendon.

Actions & Testing

The flexor pollicis brevis muscle is involved in multiple actions:

- flexes the proximal phalanx at the metacarpophalangeal joint of the thumb;

- assists in flexion of the first metacarpal bone (of thumb) at the first carpometacarpal joint.

The flexor pollicis brevis muscle can be tested by flexing the proximal phalanx of thumb at its metacarpophalangeal joint against resistance. While the proximal phalanx is held in an extended position, the flexor pollicis brevis can be seen and palpated (Moore, Dalley and Agur, 2009).

References

Moore, K. L., Dalley, A. F. and Agur, A. M. R. (2009) Clinically Oriented Anatomy. Lippincott Williams & Wilkins.